We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic ...fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-α clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans' length coherence length to be below 1.7 nG at the 2σ level, and fields coherent across the entire observable Universe below 0.65 nG. These limits do not depend on the particular origin of these cosmological fields.
Colliding wind binaries (CWBs) have been considered as a possible high-energy γ-ray sources for some time, however no system other than η Car has been detected. In the Letter, a sample of seven CWBs ...(WR 11, WR 70, WR 137, WR 140, WR 146, WR 147) which, by means of theoretic modelling, were deemed most promising candidates, was analysed using almost 7 yr of the Fermi-Large Area Telescope (LAT) data. WR 11 (γ2 Vel) was detected at 6.1σ confidence level with a photon flux in 0.1–100 GeV range (1.8 ± 0.6) × 10−9 ph cm−2 s−1 and an energy flux (2.7 ± 0.5) × 10−12 erg cm−2 s−1. At the adopted distance d = 340 pc this corresponds to a luminosity L = (3.7 ± 0.7) × 1031 erg s−1. This luminosity amounts to ∼6 × 10−6 fraction of the total wind kinetic power and ∼1.6 × 10−4 fraction of the power injected into the wind–wind interaction region of this system. Upper limits were set on the high energy flux from the WR 70 and WR 140 systems.
We made use of the two latest sets of rotation measures (RMs) of extragalactic radio sources, namely the NRAO VLA Sky Survey rotation measures catalog and a compilation by Kronberg and Newton-McGee, ...to infer the global structure of the Galactic magnetic field (GMF). We have checked that these two data sets are mutually consistent. Given the existence of clear patterns in the all-sky RM distributions we considered GMF models consisting of two components: disk (spiral or ring) and halo. The parameters of these components were determined by fitting different model field geometries to the observed RMs. We found that the model consisting of a symmetric (with respect to the Galactic plane) spiral disk and antisymmetric halo fits the data best and reproduces the observed distribution of RMs over the sky very well. We confirm that ring disk models are disfavored. Our results favor small pitch angles around ~ -- 5? and an increased vertical scale of electron distribution, in agreement with some recent studies. Based on our fits, we select two benchmark models suitable for studies of cosmic ray propagation, including cosmic rays at ultrahigh energies.
We discuss identification of possible counterparts and persistent sources related to fast radio bursts (FRBs) in the framework of the model of supergiant pulses from young neutron stars with large ...spin-down luminosities. In particular, we demonstrate that at least some of the sources of FRBs can be observed as ultraluminous X-ray sources (ULXs). At the moment no ULXs are known to be coincident with localization areas of FRBs. We searched for a correlation of FRB positions with galaxies in the 2MASS Redshift survey catalogue. Our analysis produced statistically insignificant overabundance (p-value ≈ 4 per cent) of galaxies in error boxes of FRBs. In the very near future with even modestly increased statistics of FRBs and with the help of dedicated X-ray observations and all-sky X-ray surveys it will be possible to decisively prove or falsify the supergiant pulses model.
Observations of the INTEGRAL satellite revealed the presence of yet unexplained excess in the central region of the Galaxy at energies around 511 keV. These gamma rays are produced in the process of ...positron annihilation; the needed rate is around 1042 s−1. In this short paper it is shown that β+ -emitting isotopes that are formed in interactions of subrelativistic cosmic rays with light nuclei (CNONe) can account for a considerable fraction-up to several tens of percent-of e+ production rate in the central region.
We study the phenomenology of TeV-scale black holes predicted in theories with large extra dimensions, under the further assumption that they are absolutely stable. Our goal is to present an ...exhaustive analysis of safety of the proposed 100 TeV collider, as it was done in the case of the LHC. We consider the theories with different number of extra dimensions and identify those for which a possible accretion to macroscopic size would have timescales shorter than the lifetime of the Solar system. We calculate the cross sections of the black hole production at the proposed 100 TeV collider, the fraction of the black holes trapped inside the Earth and the resulting rate of capture inside the Earth via an improved method. We study the astrophysical consequences of stable micro black holes existence, in particular its influence on the stability of white dwarfs and neutron stars. We obtain constraints for the previously unexplored range of higher-dimensional Planck mass values. Several astrophysical scenarios of the micro black hole production, which were not considered before, are taken into account. Finally, using the astrophysical constraints we consider the implications for future 100 TeV terrestrial experiments. We exclude the possibility of the charged stable micro black holes production.
We propose a novel method for observing the gravitational wave signature of supermassive black hole (SMBH) mergers. This method is based on the detection of a specific type of gravitational waves, ...namely gravitational wave burst with memory (BWM), using pulsar timing. We study the unique signature produced by BWM in anomalous pulsar timing residuals. We show that the present-day pulsar timing precision allows one to detect BWM due to SMBH mergers from distances of up to 1 Gpc (for the case of equal mass of 108 M⊙ SMBH). Improvements in the precision of pulsar timing together with an increase in the number of observed pulsars should eventually lead to the detection of a BWM signal due to the SMBH merger, thereby making the proposed technique complementary to the capabilities of the planned LISA mission.
ABSTRACT
High-energy radiation of young pulsar wind nebulae (PWNe) is known to be variable. This is exemplified by the Crab nebula, which can undergo both rapid brightenings and dimmings. Two pulsars ...in the Large Magellanic Cloud, PSR J0540–6919 and PSR J0537–6910, are evolutionally close to Crab, so one may expect the same kind of variability from the PWNe around them. In this work, we search for flaring activity in these PWNe in gamma-rays using the data from the Fermi Large Area Telescope in the range 100 MeV–10 GeV collected from 2008 August to 2021 December. We construct light curves of these sources in the three bands, 100–300 MeV, 300–1000 MeV, and 1–10 GeV, with one-week resolution. We find evidence of flaring activity in all the bands, in contrast with Crab, where no flares at E>1 GeV were observed. Analysis of the flaring episode in the 100–300 and 300–1000 MeV bands indicates that the flux of one of the PWNe could grow by a factor of ≈5–10, and the statistical significance of the flare detection reaches 6σ. We are not confident about which of the two PWNe flared because of their proximity in the sky. However, in the 1–10 GeV band, where the angular resolution of LAT is better, we find several episodes of enhanced brightness in both the PWNe. We check possible contaminants which could be responsible for the observed variability but find their contribution not to be relevant.
We study the influence of the random part of the galactic magnetic field on the propagation of ultrahigh energy cosmic rays. Within very mild approximations about the properties of the electron ...density fluctuations in the Galaxy, we are able to derive a clear and direct relation between the observed variance of rotation measures and the predicted cosmic ray deflections. Remarkably, this is obtained bypassing entirely the detailed knowledge of the magnetic properties of the turbulent plasma. Depending on the parameters of the electron density spectrum, we can either directly estimate the expected deflection, or constrain it from above. Thanks to the latest observational data on rotation measures, we build a direction-dependent map of such deflections. We find that over most of the sky the random deflections of 40 EeV protons do not exceed 1°-2°, and can be as large as 5° close to the Galactic plane.
Evidence of Fermi bubbles around M31 Pshirkov, M. S; Vasiliev, V. V; Postnov, K. A
Monthly Notices of the Royal Astronomical Society Letters,
06/2016, Volume:
459, Issue:
1
Journal Article
Peer reviewed
Open access
Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda ...galaxy M31 using almost 7 yr of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux 2.6 ± 0.6 × 10−9 cm−2 s−1, corresponding to a luminosity (0.3–100 GeV) of (3.2 ± 0.6) × 1038 erg s−1 (for a distance of 780 kpc) was found at a 5.3σ confidence level. The halo form does not correspond to the extended baryonic H i disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fitting halo template corresponds to two 6–7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the ‘Fermi bubbles’ found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star formation burst in M31.
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